Abstract

Heavy periodic loads exerted on structural materials often lead to fatigue damage (material degradation at microscale) which may finally trigger irreversible fracture process. Conventional NDT techniques detect only the latter, and there is an increasing need for new tools to assess fatigue damage at the earliest possible stage, i.e., before fracture. This paper presents experimental results of early damage characterization using an innovative nonlinear vibro‐modulation technique (VMT) [Donskoy etal., NDT&E Int. 34 (2001)]. In the experiments, fatigue damage was initiated in steel, aluminum, and carbon–carbon composite specimens during strain‐controlled three‐point bending high‐cycling fatigue tests. The damage progress was independently monitored using dataflow from the testing machine and the real‐time nonlinear vibro‐modulation measurements. The tests demonstrated that the reduction in the specimens’ stiffness (direct indication of damage accumulation) correlates well with the increase in the VMT’s nonlinear damage index. These results confirm that VMT could offer new opportunities for early damage detection and remaining life prediction. [Work supported by NAVAIR.]